Cardiac arrest (CA) is a leading cause of morbidity and mortality in the developed world. Resuscitation is attempted in an estimated 400,000 patients annually in the United States and 66 per 100,000 population every year in Europe1,2. Recovery without residual neurologic damage after cardiac arrest with global cerebral ischemia is rare. Of the few that survive to hospital discharge, >50% are left with permanent neurological sequelae3, 4. After cardiac arrest with no blood flow for more than five minutes, the generation of free radicals, during reperfusion, together with other mediators, creates chemical cascades that result in cerebral injury5. Several studies have shown that moderate systemic hypothermia (30° C.) or mild hypothermia (34° C.) markedly mitigates brain damage after cardiac arrest in dogs6-8. Two well-conducted randomized clinical trials demonstrated the benefit of cooling survivors of witnessed CA who had ventricular fibrillation (VF) as the presenting rhythm2,9. Based on these data, the American Heart Association and the European Resuscitation Council recommend therapeutic hypothermia (TH) in the management of unconscious patients following CA4,10.
Despite the strong experimental and clinical evidence, the use of TH is at best sporadic, with less than 10% of the eligible CA patients receiving hypothermia5, 11. Animal studies suggest that cooling early after ROSC is associated with improved neurological outcome and a delay in initiation of hypothermia is associated with decreased benefit7, 12. One of the important factors in rapid induction of TH is the unavailability of a reliable, easy to implement method in the field that does not interfere with resuscitation attempts. Current out-of-hospital methods to induce TH include ice-cold saline IV, ice packs2, cooling blankets13, and cooling helmets, which are ineffective to induce hypothermia. As such, there is an enormous need for a method to induce TH in the out-of-hospital setting that is non-invasive, rapid, effective, and without major harmful side effects.
The ability to induce hypothermia non-invasively and in a timely fashion is of enormous clinical value not only in cardiac arrest, but also in all threatened ischemic insults including cerebrovascular ischemia, traumatic brain injury, spinal cord injury, neonatal encephalopathy and coronary artery disease14. In cardiac arrest alone, TH will save an additional 7,500 lives per year with 50 patients treated per life saved2. Post-CA patients receiving TH gain an average of 0.66 quality-adjusted life years at an incremental cost of $31,254 due to the extended hospital stay11, which has comparable cost-effectiveness per quality-adjusted life year to many economically acceptable health care interventions.
Investigators have tried cooling the body through the nasal passages using non-compressed, low-flow air/oxygen and observed the hypothermic effect, although the mechanism behind the effect was not well understood21, 22. For example, the RhinoChill™ device achieves cooling by evaporating a coolant perfluorocarbon (PFC) in the airway or by using a volatile gas to evaporate water vapor introduced into the air to decrease the air temperature in the nasal cavity23, 24. Evaporation of the coolant PFC in the nose reportedly results in convective cooling of the brain and core body temperature.
However, ambulatory hypothermia methods relying on direct heat exchange using either cold perfusates (coolants) or surface cooling by evaporation of a volatile substance can produce excessively extreme local cooling of the exposed surfaces, at some risk to the patient. As such, such active cooling therapies are to be administered by specially trained medical technicians.
Thus, a need exists for a minimally or non-invasive method to induce TH without use of coolants or volatile substances for instance, which preferably can be used in non-medical settings, without supervision by specially trained personnel.